Best of Technical Support

Our experts answer your technical questions.
PPP on a PCMCIA Modem

My Dell arrived with factory-installed Red Hat 6.2, Kernel 2.2.14-6.1.1, and a factory-installed PCMCIA modem. All worked fine until one day, I turned on the PC and at bootup I was told:

Bringing up interface ppp0 FAILED

Somewhat later during bootup, this message appeared:

Couldn't configure serial #1 (port=760, irq=3):
  device already open
serial_cs: register_serial() at 0x2f8 IRQ 3 failed
This modem card works fine in my Gateway Windows box. Dell refuses to help. —Steve Lohr, steve@azstarnet.com

It's possible you have a program running that is tying up your serial port. Two common culprits are GPM, the text mouse dæmon, and one of several UPS monitoring dæmons. Use the ps ax | less command to look for such culprits. If you are still having problems identifying the culprit, try booting into single-user mode to shut down all unnecessary programs. Then use minicom to access the port directly, and verify that it can see your modem. —Chad Robinson, crobinson@rfgonline.com

Perhaps a lock still exists from a previous session not ending normally. See if there are any old lock files in /var/lock, such as LCK..modem or LCK..ttyS1. If there are, just delete the files and reboot. —Keith Trollope, keith@wishing-well.demon.co.uk

I Have No Nameserver and I Must nslookup

I am setting up a Linux machine that will masquerade my workstations and provide port-forwarding to my web/mail server. My question is, do I need an internal DNS server on my Linux machine to serve up DNS requests in order to browse the Web on my internal workstations? I would rather use the hosts file to define name-to-IP translations of my internal network. —Brandon Zumwalt, bzumwalt@seventhview.com

You do not need a DNS server on your Linux box, but you also cannot use the hosts file to perform this lookup. The hosts file is used by services running on your Linux box itself. Your first option is to configure your internal systems to use the DNS servers provided by your ISP. Once you have masquerading set up properly, your workstations will be able to access them and resolve web addresses without further work. Alternatively, you can set up a DNS server on the Linux box that will cache workstation requests. If you want to simplify this configuration, use the forward-only sample configuration for BIND. That puts the server into caching-only mode, with no local tables of its own. —Chad Robinson, crobinson@rfgonline.com

Check your distribution's site for BIND security updates. Old versions of BIND, like the one that's probably on your distribution CD-ROM, are subject to automated attacks. Or run—Don Marti dmarti@linuxjournal.com

X and Sound over the Net

Is there a way I can have an X window appear on more than one X server (display)? I may want to do it (perhaps read-only) for, say, DVD output to displays throughout my home.

Separately, when I run an X application from a remote machine, how can I get the sound to follow and output on my local sound device? I only seem to be able to get sound out of a configured sound card for the host that owns the application. Similar to the above, can this be redirected to more than one address (back to my DVD playing in every room fantasy)? —Matthew Holmy, mholmy@yahoo.com

Xmx will allow you to display a normal X application on several X displays, http://www.cs.brown.edu/software/xmx/. However, for display speed reasons, some applications (like DVD players) bypass most of the X server when they write to your video card. Unless they have a slow, normal display mode, you can't do a remote display. You cannot send full framerate uncompressed video over Ethernet; it's too much data. You should, however, be able to rip a DVD on one machine, send it over the network and play it from disk on a different one. The network audio system lets you play sound over the network, radscan.com/nas.html. Another program you can look at is located at http://rplay.doit.org/. —Marc Merlin, marc_bts@valinux.com

make Just One Module?

I recently acquired a USB scanner (Epson Perfection 1640SU) and was successful in getting it to work with my Linux system (kernel 2.2.16-22). However, I need to modify one of the timeout parameters in scanner.h in the kernel source. How do I recompile this module to get scanner.o without having to recompile the entire kernel? Do I make a backup of /lib/modules/2.2.16 before I do this, and can it be safely restored in case of error? —Jin, j.r.ong@ieee.org

After modifying the file, simply type make (target), e.g., make bzImage, from your /usr/src/linux or similar directory. This will recompile only the necessary files. The Makefile set for Linux has been altered to always compile certain files, such as main.c, but only a few files fit that category. All of the drivers should be skipped except the one you've changed. If you've changed only the .h file, the make program may not recompile your driver. Try touch scanner.c to simulate having made changes to the file. In addition, you can make your life a lot easier by simply using a module instead, in which case you would not need to recompile the kernel, only rerun—Chad Robinson, crobinson@rfgonline.com

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